CVE-2021-28697

Guest-to-host compromise via grant-table mapping race

Published Aug 27, 2021 · Updated Aug 3, 2024

Race condition in Xen Hypervisor 4.0 and later allows guest OS users to access freed hypervisor memory via racing mapping requests. The grant-table code tracks only one guest mapping for each v2 status page, so concurrent insertions can leave another mapping untracked when the page is deallocated. Only x86 HVM or PVH guests allowed to use grant table v2 can trigger the race, enabling host privilege escalation, information disclosure, or host and guest service interruption.

CVSS severity7.8
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Xen Hypervisor 4.0 and later allows guest OS users to access freed hypervisor memory via racing mapping requests. The grant-table code tracks only one guest mapping for each v2 status page, so concurrent insertions can leave another mapping untracked when the page is deallocated. Only x86 HVM or PVH guests allowed to use grant table v2 can trigger the race, enabling host privilege escalation, information disclosure, or host and guest service interruption.

The record

CVE
CVE-2021-28697
Published
Aug 27, 2021
Updated
Aug 3, 2024
Vendor
Xen Project
Product
Xen Hypervisor
Classifications
CWE-362, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.11.x <unspecified
  2. Affected versionversion=4.13.x <unspecified
  3. Affected versionversion=4.15.x
  4. Affected versionversion=xen-unstable

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Xen Project · Xen Hypervisorversion=4.11.x <unspecified; version=4.13.x <unspecified; version=4.15.x; version=xen-unstable

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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